Two-way telephone and telegraph system



July 4, 1944.

J; E. SMITH Two-WAYJTELEPHONE AND TELEGRAPH SYS-TEM Filed oct. 50, 1.942

- propagation constant.

monica Joly 4, 1944 J. Ernest smith, Jackson Heights, N. Y., nssignor'to Radio Corporation of Americaa corporation of Delaware Applicationoctober 3o, 1942, serial No. 463,883

' 12 claims. (ci. 179-4) This invention relates to two-way telephoneandtelegraph systems, and more particularly t0 a device for improvingthe :transmission characteristics of a combined telephone and telegraphcircuit., The improvements havefor their principal object to minimizethe effectsof outside 4'interferenceupon telephone andy telegraphchannels and to overcome the effect of a variable In the past, where theline consisted of a twistthe received -signal varies greatly withweather conditions, theinfluence of the earth's magnetic ileld. andinduced noiseinterference. Where a telegraph signaling system is to becombined j ed pair of conductors, it has been.. found that with atelephone circuit, it has been a common i.

practice lto terminatel the transmission line at both ends by atransformer havingga center-tap through which telegraph signals might besent and received. The telegraph signals would thus be conveyed over thetwo conductors of the twistled pair the same as if they were a singleconductor. The telegraph apparatus at each station lwould be grounded,thus completing the telegraph circuit. The telephone circuit wasoperated in a conventional manner, voice signals being induced on theindividual conductors of the twisted pair 1n phase opposition. Thediiliculties encountered were not so much due to interfervence betweenthe telephone circuit and the tele- Will preferably pass any frequencybelow 250 20.

lcircuit arrangement including apparatus units which are vsuitablycombined at a single station and rendered operable both. fortransmission and .reception of telephone and telegraph signals; and Fig.2 shows a modified circuit arrangement.

Referring to Fig.- 1, I show therein a line I terminating in atransformer winding 2 which is inductively coupled to a winding 3 in thesame transformer. A Ahigh-pass filter 4 is interposed between thetransformer winding 3 and terminals 5 leading, say, to a telephoneinstrument having a microphone andan earphone. The characteristics ofthe filter I are preferably those .which will pass speech signalsabove afrequency of 250 cycles and will eifectually block any frequencies below250 cycles. For telegraph signaling, a low-pass filter 6 may be used.This filter cycles.' o

The lters 4 and 8 are so designed that energy maybe fed'into them fromeither end. They will,'therefore, be uniformly eflicient fortwowaycommunication work. So far as the transformer winding 3 is concerned,this is connected l to the right hand terminals of filters 4 and 6 ingraph circuit, as they were due to unstable lground return effects suchas might'be produced by the earths magnetic field. Furthermore, theemciency of the-telegraph circuit was limited by a high degree ofattenuation of the received signals. The telegraph system was `alsosubject to erroneous operation due to induced noise interference on theline.

' Accordingly, it is an object of my invention to provide a two-waycommunication system having a twin conductor circuit over whichtelephone and telegraph signals may be transmitted simultaneouslv, andwhereinfthe .signal propagation shall be rendered relatively independentof outside influences.

Itis another object of my invention to provide a system of the classdescribedv whichovercom'es the adverse effects of attenuation in a longline 'and which requires a minimum vof terminal apparatus foraccomplishing this result.

Other .objects and advantages of my invention will be made apparentinthe description to follow. This description is accompanied by adrawing, in which: Fig. 1 shows in diagrammatic form a preferredparallel. The left hand terminals of filter B are branched. One branchleads to the input side ofl an amplifier limiter device 'I which isuseful for amplifying the received telegraph signals. 'I'he output sideof the amplifier 1 is again branched and leads to two parallel-connectedfilters Q and 9. Filter 8 has a high-pass characterlstic ,for passingfrequencies above 125 cycles,

/e. Filter 9 has a low-pass characteristic and passes frequencies belowcycles, for

for examp example.

'I'he telegraph signals to be transmitted and received will preferablybe composed of two distinguishable frequencies.- For the sake ofillustration, the marking frequency is indicated -as cycles, while thespacing frequency may be 100 cycles. Accordingly, the marking frequencywill be passed by filterV 8 and after rectification in'the rectifier i0,the rectified energy maybe caused to traverse one winding il of apolarized relay. 'I'he two windings il and i2 of this relay areterminated in acommon ground connection. Winding i2 is fed withrectified energy through the rectifier I3 in the output circuit offilter 9.

The tongue I l of the polarized relay cooperates with stationarycontacts oneof which may be dead, while the other contact i5l is fedwith'a positive potential from any suitable source. The i' relay tongueI4 may be connected to the respontionary contact I5. In this manner amarking impulse is impressed upon the responsive means inthe receivingprinter I6. As is well'known,

such responsive means may consist of selectorsv suitable for causing theprinter to record characters corresponding'to a train oftelegraphsignals.

The various terminal apparatus units thus far described are -used ateither stationfor the reception of telegraph code signals. Thetransmitting apparatus is preferably the same at the two stations andwill now be described.

A conventional code keyer I1 is. indicated as having five movablecontacts I8 for composition of the well-known five-unit code signals.Such signals may be delivered by a manually operated keyboard or by aperforated tape sensing device. The code keyer also comprises aso-called startstop contactor 2li if desired. -In place of the codekeyer,v as represented, a simple hand-operated telegraph key may beused, or more elaborate apparatus such as a synchronous signalingsystern may be adopted if desired, the same as in multiplex telegraphy.In any case, the signals as transmitted may be characterized by twofrequencies, say of 150 cycles for marking impulses, and of 100 cyclesfor spacing impulses.

A relay I8. has its winding connected between ground and a conductorwhich is alternately fed by positive and negative impulses in accordancewith the permutational setting of the five code contacts I againstpositive or negative stationary contacts in the keyer -I1. Inconventional stop-start five-unit code keyers, each five-unit codesignal is always preceded by a spacing impulse and followed by a markingimpulse. The start impulse is produced, therefore, by movement of thecontact tongue 2Il'from its positive to its negative stationary contactin the keyery I 1. The tongue 2I of relay I8 responds to code keying bythe unit I1 and thus feeds current of different frequencies to theoutput circuit 22. The marking and spacing frequencies are preferablyderived .from two` separate oscillators 23 and 2l, each connected to arespective one of the stationary contacts which are associated with therelay tongue 2 I. One output terminal in each of these oscillators maybe grounded if desired.

The signals are composed by the keyer I1 and as characterized for markand space bythe osci1;

lators 23 and 24 may beapplled through a capacitor 25 to the inputcircuit of an amplifier 2l.

The output circuit for this amplifier is connected to a double-polesingle-throw switch 21, this*l switch being closed when transmitting.The conductors 28 connect the upper terminalsof switch 21 to the lefthand terminals of the lowpass filter 6. These signals are, therefore,ap-

- plied'to the transformer winding 3, now operating as a primary, andthey are thus coupled to the terminating transformer winding 2 in theline I.

In place of the oscillators 23 and 2l, itis apparent that I may ifdesired utilize a single oscil-A lator, thel tuning of whichrnay bevaried by a switching operation under control of the relay I8. In thisway the invention may be carried out Avery simply by providing a certainfixed tuning for the closed tank circuit ofthe oscillator, and byswitching on and off an added capacitance filter 6 has one of itsterminals grounded and the other terminal is connected to a center tapon the winding 2a. The telegraph signaling channel is such, therefore,that the signals are transmitted co-phasally over the two conductors ofthe line I',-and ground connections are required at both. stations forthe return circuit.

Since identical terminal equipment may be used at the two ends of theline, there is no need to describe other apparatus than merely thatwhich exists for transmission and reception at one station. It isapparent also that for use of the telephone circuit, it is unnecessaryto show the actual telephone equipment which would be employed, sincethat equipment may be of any conventional type.

While I have illustrated my invention and described its components andits mode of operation in accordance with only two exemplary embodiments,it is to be understood that I do not intend to be limited to the use ofthe equipment which is herein shown and described. I claim:

1. In a communication system, a two-way station comprisingsimultaneously operable telephone and'telegraph apparatus, atwo-conductor ltnea high-pass filter offering a low impedance totheuseful frequency bandof telephone signal's,.a l'w-pass filter offering alow impedance phone set coupled to said line through said highpassfilter, and telegraph signaling apparatus coupled to said line throughsaid low pass lter,

` said telegraph signaling apparatus having frequency-characterizingmeans for distinguishing between the marking and spacing elements ofoutgoingcode signals and frequency discriminating telegraph signalresponsive means adapted and arranged to accept and translate incomingcode signals.

2. A two-way communication station according to claim 1, wherein saidfrequency discriminating means includes filters the input terminals ofwhich are parallel-connected, said filters having cut-off points whichlie between the characteristic marking and spacing frequencies of theincoming code signals.

3. A two-way communication station according to claim 1, wherein saidfrequency discriminating means includes a vhigh-pass filter for ac.

cepting the frequency of the marking code elements, and a low passfilter for accepting the frequency of the spacing code elements, thefrequency bands passed by the last mentioned filters being mutuallyexclusive. and said responsive means including a polarized relay havingoppos- 'ing windings each in circuit with the output terminals of one ofthese filters respectively, and means for rectifying the alternatingcurrent output from these filters, thereby to energize said relaywindings with rectified potentials.

4. A system for composite telephony and telegraphy over a twin-conductorcircuit, said system comprising filter means for passing telephone'frequencies and for excluding telegraphic tone signal frequencies,filter means for passing said telegraphic tone signal frequencies andfor excluding said telephone frequencies, the differtwo tone frequencyoscillators in said transmitter, andkeying means operable to delivertone signals from said oscillatorsl at alternate intervals correspondingto said marking and spacing code elements.

6. A composite telephone 'and telegraph system comprising a plurality ofstations in each of which transmitting and receiving devices are coupledto a communicationchannel, the transmitting ldevices including separatetelephone and telegraph instruments, and the receiving devices alsoincluding separate telephone and telegraph instruments, filter meansappropriate to the circuits of saidtelephone instrumentsand arranged fortwo-way passing of voice frequencies between said telephone instrumentsand said channel, and other filter means appropriate to the circuits ofsaid telegraph instruments and arranged for twoway passing of certaintone frequencies allocated to telegraph code signals, the frequencybands passed by the two said filter ,means being mutually exclusive,said telegraph transmitting instruments including means and a coderkeyer arranged to feed tone frequency energy of different predeterminedfre.

quencies from said generating means through said other filter means tosaid channel, and said telegraph receivingapparatus having frequencyselective means and rectiflers for translating said certain `tonefrequencies into signaling code elements of marking and spacingsignificance.

7. A system in accordance with claim 6 and including an amplifierlimiter device in circuit between said other filter means andv saidfrequency selective means.

8. A system in accordance with claim 6 and including a switch fordisconnecting said tone-fre-l quency generating means from said otherfilter means during reception ofl telegraph signals from a remotestation.

9. Apparatus for signaling by simultaneous telephony and telegraphy,comprising a communitone-frequency generating cation channel extendingbetween two stations, telephone filter means at both stations forpassing speech frequencies above a predetermined filter cut-ofi' pointto and from said channel, said Vfilter means being reactively coupled toconductive elements in said channel, telegraph filter means at bothstations for passing two tone frequencies which lie in a frequency bandbelow said cut-off point, said telegraph filter means beinginterconnected through ground and through conductive elements in saidchannel, means at each station for generating and keying said tonefrequencies, thereby to transmit intelligence, and translating means ateach station arranged to accept incoming telegraph signals which arecomposed of marking and spacing ele,- ments differentiated by said tonefrequencies, said translating means including frequency selectivefilters each of which is arranged to accept an appropriate one of saidtone frequencies and to reject the other.

10. Apparatus' according to claim 9 and including a transformer at eachstation, one winding in each transformer being terminally connected tosaid telephone Afilter means and the other winding being'terminallyconnected to parallel conductors in said channel.

, 11.- Apparatus according to claim 9 and including avtransformer ateach station, one winding in each transformer being connected across Yterminals at one end of each said telephone filter means, and the otherwinding in each transformer being center-tapped and being connectedacross two conductorsin said channel, the center-tap being connected toa terminal at one end o f the adjacent` telegraph filter means, and a'ground connection to the remaining terminal at the same end of saidtelegraph filter means.

12. The method of signaling by simultaneous telephony and telegraphyover a given communication channel, and by using said channel as atwo-way system, which method comprises restricting speech waves ascommunicated to and from said channel to a band of frequencies above apredetermined filter cut-off point, restricting telegraph signals ascommunicated to and from said channel to two distinct tone frequencyallocations both of which lie below said cut-ofi' point, generating saidtone frequencies to represent the marking and spacing connotationsofsignal code elements, and translating such signal code elements whenreceived at a given station by filter discrimination between the twosaid tone frequencies.

J. ERNEST SMITH.

